In continuous casting apparatus such as shown in U.S. Pat. Nos. 4,000,773, 4,178,982, 4,285,388, the casting apparatus conventionally utilizes a tubular die having an inlet through which the molten metal is introduced and an outlet through which the hot solidified cast product is removed, surrounded by a cooling assembly. In the start up of such apparatus, it is conventional to utilize a starting bar which supports a starter tip that draws the solidified metal axially between opposed sets of rolls, one set of which is mounted for rotation about a stationary axis and the other set of which has the rolls mounted for rotation about axes movable radially inwardly and outwardly.
In the operation, the starter tip is inserted in the tubular die and the starting bar is drawn axially by the rolls bringing the first portion of the cast product between the rolls.
The starter bar is made of a nominal size tube so that it is light in weight and economical to construct. The starter bar on vertical or horizontal machines varies in length from four feet up to 12 feet and in diameter from 1" up to 12". For economic reasons the starter bars are made of light tubing and have to be very straight and must be able to withstand the pressure of pinch rolls or the pulling jaws. The end of the starting bar is provided with a plug and a threaded bore to receive the starter tip. The starting bar and the starter tip have the same center line when they are assembled together. If the rolls are initially positioned to grip the starting bar, there will be a tendency to force the stationary rolls radially since the hot cast product expands upon leaving the die and has a diameter greater than the diameter of the starting bar. Since the one set of rolls is stationary, the cast product will be pulled downwardly but the center line of the product will tend to be shifted radially from the stationary rolls and the center line of the die. This causes a wave or sinuous configuration of the cast product and tends to apply lateral forces on the die. In addition, the tendency of the cast product or bar to move in a sinuous path tends to move portions of the product away from the die resulting in hot spots in the cast product which often causes a re-melting at these hot spots with a resultant interruption of the casting operation. In addition, the movement of the cast product tends to break the seal around the die with resultant leakage of hot metal at the top of the cooling assembly causing an interruption in the operation.
If the casting operation is not interrupted, the sinuous movement of the cast product produces a hot spot which will revolve about the periphery of the resultant cast product and produce a lack of homogeneity and a defective outer skin surface. More specifically, the hot spot tends to cause separation of the constituents of the molten metal and cracking on the outer surface.
In order to be able to start each nominal outside diameter of cast product, the same size of nominal starting bars are fabricated. Many times the starting bars are made from the same material as the cast products. This makes the bars heavy and cumbersome, difficult to straighten and not economical to stock.
Because of the aforementioned problems other standards have been adapted and an extra amount of stock added on the outside and inside diameter of the cast products.
Thus, for example, the additional material may be from 0.03 to 0.135 inch for outside diameters ranging between one inch and five inch. In the case of diameters over five inch, added material on the order of one-eighth to one-fourth of an inch is provided. In the case of the inside diameters on tubular products, additional material is provided on the order 0.060 inch for a one inch diameter up to one-fourth inch on larger diameters. This additional material not only requires machining which adds to the cost, but also results in increased scrap that increases the cost.
Where the products being cast have heavy walls or large diameters, the pulling forces must overcome substantial friction within the die. Failure to move the material which has been solidified on each stroke of the rotating rolls will result in stoppage of the casting operation or breaking of the die or breaking of the mandrel in the case of tubular products.
Accordingly, among the objectives of the present invention are to provide a starting bar assembly for continuous casting apparatus which functions vertically or horizontally and in casting upwardly or downwardly, which will result in maintaining the center line of the cast product aligned with the die; which obviates the need for individually sized starting bars and the resultant added cost and inventory; wherein the center line can be adjusted to accommodate differences in diameters; and which obviates the need and expense of straightening the cast products or otherwise substantially machining or reshaping the products; and which improves the efficiency of the casting operation.
In accordance with the invention, a starter tip being dimensioned to fit within the die is interconnected to a starting bar for adjustment radially relative to one another such that when the starter tip is inserted into the tubular die upon start up of the casting apparatus, the movable drawing rolls can be successively moved radially inwardly or outwardly with respect to the center line of the cast product to maintain the center line of the cast product aligned with the center line between the opposed sets of rolls.